The project aims at obtaining an understanding of the extrinsic regulations, humoral and cellular, that apply to neurons and glia cells during development and adult life. The objective will be pursued by the establishment and investigation of dissociated neural cell systems and cultures mimicking in vitro properties of the source tissues and yet readily susceptible to experimental manipulation. Source tissues will be mainly dorsal root ganglia, sympathetic ganglia, ciliary ganglia and spinal cord from embryonic chick and newborn rodent. Neurons and glial cells, as well as some peripheral tissues, will be examined as putative sources of macromolecular neuronotrophic and gliotrophic agents, whose properties will be compared to those of Nerve Growth Factor (NGF). The investigation of NGF will be continued toward an elucidation of its mechanism of action, particularly with regard to the interaction of the factor with the plasma membranes of its ganglionic cell targets.